Flow Cytometry As a Novel Tool to Evaluate and Separate Vesicles Using Characteristic Scatter Signatures

Giant Unilamellar Vesicle Electroformation: What to Use, What to Avoid, and How to Quantify the Results

Since its inception more than thirty years ago, electroformation has become the most commonly used method for growing giant unilamellar vesicles (GUVs). Although the method seems quite straightforward at first, researchers must consider the interplay of a large number of parameters, different lipid compositions, and internal solutions in order to avoid artifactual results or reproducibility problems. These issues motivated us to write a short review of the most recent methodological developments and possible pitfalls. Additionally, since traditional manual analysis can lead to biased results, we have included a discussion on methods for automatic analysis of GUVs. Finally, we discuss possible improvements in the preparation of GUVs containing high cholesterol contents in order to avoid the formation of artifactual cholesterol crystals. We intend this review to be a reference for those trying to decide what parameters to use as well as an overview providing insight into problems not yet addressed or solved.

Screening and Quantification of the Encapsulation of Dyes in Supramolecular Particles

The encapsulation of therapeutic agents, such as drugs and vaccines, into colloidal particles offers an attractive strategy to enhance their efficacy. Previously, we reported the development of guanosine-based supramolecular colloidal particles suitable for encapsulating a broad array of guests ranging from small molecule drugs, like doxorubicin, to proteins, like GFP. Many biomedical applications of such particles require a precise determination of the amount of encapsulated therapeutic agents. Despite many studies describing the development of particle-based delivery systems, a general method for the precise and quick quantification of the encapsulated payload is still lacking. Here, we report a method based on flow cytometry measurements for complexes made from guanosine-based particles and a variety of commercially available fluorescent dyes. This method allows us to determine the apparent affinities of such dyes for two variants of these particles, which in turn provides insightful structure-affinity relationships. In contrast to the current methods, such as those that rely on fluorescence microscopy based on measurements of absorption/fluorescence of dissolved particles or on the supernatant of the solution, the reported method is suitable for high-throughput screening and more reproducible results. The protocol described here should be applicable to a wide variety of colloidal particles being developed around the world. Our group is currently expanding the scope to quantify the encapsulation of other molecules of biomedical interest, such as proteins and nucleic acids.

Microfluidic methods for forming liposomes

Liposome structures have a wide range of applications in biology, biochemistry, and biophysics. As a result, several methods for forming liposomes have been developed. This review provides a critical comparison of existing microfluidic technologies for forming liposomes and, when applicable, a comparison with their analogous macroscale counterparts. The properties of the generated liposomes, including size, size distribution, lamellarity, membrane composition, and encapsulation efficiency, form the basis for comparison. We hope that this critique will allow the reader to make an informed decision as to which method should be used for a given biological application.

Flow cytometry-based evaluation and enrichment of multiwalled carbon nanotube dispersions

The uniform aqueous dispersion of carbon nanotubes (CNTs) is a vital but challenging task required for their utilization in most technologies. We propose and demonstrate a technique based on forward- and side-scatter analysis on a flow cytometer to characterize the components in a dispersion of multiwalled CNTs (MWCNTs). The method simultaneously distinguishes various MWCNT components such as short and long CNTs, nanotube bundles, and particulates. It also detects the emergence of new CNT populations as a result of centrifugation. We use this method, together with classical methods such as UV and Raman spectroscopy, to observe and study the multistep MWCNT dispersion process in various surfactants (Pluronic, Triton X-100, sodium dodecyl sulfate, and cetyl trimethylammonium bromide). On the basis of the distinct scatter patterns obtained, we confirm and elaborate the surfactant-assisted unzipping mechanism of MWCNT dispersion. We also show that the ultrasonic energy spent after MWCNT unbundling and unwinding can be minimized and the process optimized for each surfactant by correct end point detection through scatter analysis. The ability to enrich nanotube population in dispersion by using the sorting mode of a flow cytometer is confirmed by electron microscopy and Raman spectroscopy. This method can thus be used for observing and enriching MWCNT components and as a complementary technique to UV spectroscopy for studying and optimizing MWCNT dispersion in surfactants.